Vocal forgery in forensic sciences

Abstract

This article describes techniques of vocal forgery able to affect automatic speaker recognition system in a forensic context. Vocal forgery covers two main aspects: voice transformation and voice conversion. Concerning voice transformation, this article proposes an automatic analysis of four specific disguised voices in order to detect the forgery and, for voice conversion, different ways to automatically imitate a target voice. Vocal forgery appears as a real and relevant question for forensic expertise. In most cases, criminals who make a terrorist claim or a miscellaneous call, disguise their voices to hide their identity or to take the identity of another person. Disguise is considered in this paper as a deliberate action of the speaker who wants to conceal or falsify his identity. Different techniques exist to transform one's own voice. Some are sophisticated as software manipulation, some others are simpler as using an handkerchief over the mouth. In voice transformation, the presented work is dedicated to the study of disguise used in the most common cases. In voice conversion, different techniques will be presented, compared, and applied on an original example of the French President voice. © ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2009.